This invention relates generally to fluid manifolds, and more particularly to fuel manifolds in gas turbine engines.
A gas turbine engine includes a turbomachinery core having a high pressure compressor, a combustor, and a high pressure turbine in serial flow relationship. The core is operable in a known manner to generate a primary gas flow. Depending on the engine's configuration, the core may be combined with a fan and low pressure turbine system to generate propulsive thrust, or with a work turbine to extract mechanical energy and turn a driveshaft or propeller.
In conventional gas turbine engines, fuel is introduced to the combustor through an array of fuel nozzles which are coupled to an annular external manifold surrounding the combustor and mounted to a combustor case. In operation, pressurized fuel is fed to the manifold. The manifold then distributes the pressurized fuel to the individual fuel nozzles through individual feed lines. Such manifolds are commonly manufactured from various tubes and fittings, and are secured to the combustor with brackets and other mounting hardware.
Aircraft engine fuel manifolds are in a harsh environment and are located relatively close to the combustor case. The combustor case grows as the engine warms, but the temperature of the fuel in the manifold stays relatively cool. This temperature difference, coupled with the different material growth rates of various components, creates a thermal loading on the manifold. In a conventional manifold the length of piping between mounting points (i.e. the nozzle-to-nozzle distance) is fixed, limiting the length of piping available to provide flexibility.
It is also known to provided “staged” fuel delivery systems which include two or more fuel circuits used during different engine operating conditions (e.g., pilot and main circuits). In a conventional fuel manifold, each circuit or stage requires separate piping and connections, increasing weight, complexity, and parts count. Furthermore, the fuel passages within the manifold and other piping are subject to undesirable carbon buildup (“coking”) of the residual fuel during periods of time when fuel is not flowing in a particular circuit.
Accordingly, there remains a need for a fuel manifold which accommodates thermal growth and provides for staged fuel flow which avoiding coking.